1. Field of the Invention
The present invention relates to a fixing belt, a fixing device, and an image forming apparatus.
2. Description of Related Art
Conventionally, electrophotographic image forming apparatuses including copiers, and laser beam printers employ fixing devices in which a heated fixing belt is brought into contact with a transfer material bearing an unfixed toner image to fix the toner image to the transfer material. As such fixing devices, a fixing device having a fixing belt, and two or more rollers including a heating roller and pivotally supporting the fixing belt (e.g., Japanese Patent Application Laid-Open No. 2006-317505: Patent Literature 1; hereinafter, referred to as PTL 1). Since the fixing belt has relatively small thermal capacity, the fixing belt is excellent in fixing a toner image to a transfer material, and thus contributes to the speedup of image formation.
The fixing device in the image forming apparatus disclosed in PTL 1 includes an endless fixing belt, a fixing roller and a heating roller pivotally supporting the fixing belt, a pressure roller being pressed toward the fixing roller with a predetermined pressure with the fixing belt being interposed therebetween, and a local heating means that heats the heating roller. In the image forming apparatus disclosed in PTL 1, when a transfer material is nipped by the pressure roller and the fixing belt heated by the heating roller, wax contained in toner is melted to exude to the transfer material to thereby fix the toner image to the transfer material. At this time, the contact between the fixing belt and the transfer material allows the temperature of the fixing belt to be lowered temporarily. The fixing belt whose temperature is lowered is heated to the original temperature by the local heating means. Thus, the image forming apparatus disclosed in PTL 1 forms an image without gloss unevenness by keeping the temperature of the fixing belt constant when fixing the toner image.
However, in the image forming apparatus disclosed in PTL 1, consideration is given neither to the difference in the decrement in temperature between areas of the fixing belt corresponding to areas of the transfer material on which an image is formed and on which an image is not formed, nor to the temperature of the fixing belt in the case of continuous printing of transfer materials of different sizes. That is, the image forming apparatus disclosed in PTL 1 has a room for improvement in gloss unevenness.